Preparation Of Confined Ion Exchange Membranes And Study On Desalination Of High Salinity Organic Wastewater

With the acceleration of industrialization,many industries produce high salinity organic wastewater,which contains a large number of recyclable resources and harmful pollutants to human health or the environment.Exploring an advanced technology for treating high saliinity organic wastewater is of great significance for protecting ecological environment,promoting circular economy and alleviating resource shortage.Electrodialysis（ED）technology has become a mature technology for treating high salinity organic wastewater because of its unique advantage（superior selective separation performance）.As a key component of electrodialysis technology,ion exchange membrane determines the development of electrodialysis technology to a large extent.In order to recover high concentration salt from high salinity organic wastewater,this study ion exchange membranes with good cofined meachnism for organic and water were pepared to treat high salinity organic wastewater,explored the effects of different sulfonation degrees on desalination performance,organic matter retention performance and separation performance of salt and organic matter,investigated the effects of organic matter on salt migration and water transport,and analyzed the salt-water-organic matter transport nexus and mechanism.In addition,this study also added hydrophobic compounds into the ion exchange membrane in order to improve the concentration of recycled salt.A simple model was proposed to evaluate the water transport performance of the membranes,and the influence of hydrophobic compounds on salt and water transport was explored.The main research contents and conclusions are as follows:（1）A series of cation exchange membranes（CEMs）were prepared using sulfonated polysulfone with different sulfonation degrees as matrix material as a tool to"adjust"membrane water absorption and"control"water migration.The surface properties,desalination properties,organic matter retention performance and separation performance of organic matter and salt of the membranes were characterized and evaluated,and the salt-water-organic matter transport nexus and mechanism were analyzed.The results showed that the CEM with high sulfonation degree was positively correlated with the desalination performance.In particular,the desalination rate of cofined ion exchange membrane with 50%sulfonation degree（15.67%）was 3.5 times that of the commercial membrane SYMC-2（4.46%）,and also showed high organic permeability.Reducing the degree of sulfonation can effectively improve the separation performance of organic matter and salt.In particular,the separation effect of cofined ion exchange membrane with 50%sulfonation degree on NaCl and PEG600 was 75.93%higher than that of SYMC-2.It had also been shown that salt migration leaded to organic matter migration,while the presence of small molecules of organic matter reduced water flux and increased sodium flux,which was beneficial to the ED process.The main reason was that organic matter was attached to Na⁺for electromigration,and carried water through the membrane.It was proved that the membrane sulfonation degree can be used as an important factor to regulate water penetration,so as to improve the separation performance of salt and organic matter in wastewater.（2）Taking the sulfonated polysulfone with 50%sulfonation degree as the substrate material,adding the hydrophobic compounds to prepare the CEMs,and applying the membrane in the electrodialysis system,a simple model was proposed to evaluate the water transport performance of the membrane.Based on the mass transfer study,the characteristic parameters of the model were obtained by changing the osmotic pressure and applied voltage on ED stack.In addition,the effect of osmotic pressure on salt diffusion and the effect of current density on salt migration were investigated,and the desalination performance of the membrane was evaluated and compared with that of the commercial SYMC-2.The results showed that,compared with the base membrane（the membrane with 50%sulfonation degree:SPSU50）,the desalination performance of the membrane was not weakened after adding hydrophobic substances to the membrane,and the ion migration rate and desalination rate of the membrane were still similar to SPSU50.The linear relationship between Na⁺flux and current density（R²>0.99）proved that the salt flux in electrodialysis process was caused by the migration of potential gradient,and the contribution of diffusion to salt flux was negligible.It was also found that the addition of hydrophobic compounds weakened the permeability and electropermeability of the membranes,but the permeability of the membranes was still higher than that of SYMC-2,and the interception of water was improved,especially the electropermeability coefficient of the ion exchange membrane with Si O₂ added to the base membrane was 0.69 times that of SPSU50.This study proved that the water uptake of ion exchange membrane can be controlled by adjusting the sulfonation degree,so as to realize the separation of organic matter and salt.In addition,the addition of hydrophobic compounds to the membrane can achieve reducing water transport.It provided a reference for preparation of ion exchange membrane which can be used to improve the concentration and purity of recovered salt in ED treatment of high salinity organic wastewater.